This invention relates to smoke/fire dampers and particularly to butterfly type dampers for use in air ducts.
It is important that a smoke/fire control damper by capable of withstanding intense heat and/or air pressures which impinge on either side of the damper for substantial periods of time during a fire. Due to the extreme conditions to which such a damper is subjected, it is necessary to provide a fire capable blade and frame design which together form a tight positive seal to effectively shut off the air duct, opening or plenum.
In fact, due to this deficiency experienced by some practitioners in this field, folding blade fire dampers such as those illustrated in my previously issued U.S. Pat. Nos. 3,866,656; 3,866,657; 3,814,165; 3,401,734; 3,727,663; 3,327,764; and 3,273,632 have been utilized in order to overcome those deficiencies otherwise encountered by some devices utilizing a plurality of rotating blades, each of which blades must form a seal with an adjacent blade as well as the frame, which seal is sometimes prone to leakage in the event that extremely precise alignments and tolerances are not maintained. This problem has been aggravated by the fact that smoke and fire dampers must function effectively in a relatively dirty environment years after they have been installed.
Prior art rotating blades fire and smoke dampers have, therefore, incorporated extremely heavy materials which are not subject to easy bending or deformation in the presence of heat. The blades are mounted by distinct hinge or pivot means which are separately installed for the purposes of aligning each of the blades for rotational movement and to ensure the interengagement of each blade with its adjacent blade to form a seal therebetween which does not open in the presence of heat or excessive pressures, such as those which might be encountered during a fire.
It is sometimes desirable to provide dampers with springs for forcing the blades of a folding blade or a single blade damper to the closed position. My previously issued U.S. Pat. Nos. 3,899,156; 3,866,657; 3,814,165; and 3,401,734, illustrate various uses of springs in this regard. Spring closure devices when they used, are normally mounted at one end of the frame to pull curtain-type folding blade closures thereacross; or on one side of a single blade to cause that blade to engage a locking clip to lock it in the closed position. Springs have not generally been used (in the absence of the locking device) to directly restrain the devices against fire since heat will tend to cause the spring to lose its strength, and thus its effectiveness.